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1 /*
2 * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
3 * The President and Fellows of Harvard College.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30 /*
31 * crt0.o for MIPS r2000/r3000.
32 *
33 * crt stands for "C runtime".
34 *
35 * Basically, this is the startup code that gets invoked before main(),
36 * and regains control when main returns.
37 *
38 * All we really do is save a copy of argv for use by the err* and warn*
39 * functions, and call exit when main returns.
40 */
41
42 #include <kern/mips/regdefs.h>
43 #include <kern/syscall.h>
44
45 .set noreorder /* so we can use delay slots explicitly */
46
47 .text
48 .globl __start
49 .type __start,@function
50 .ent __start
51 __start:
52 /* Load the "global pointer" register */
53 la gp, _gp
54
55 /*
56 * We expect that the kernel passes argc in a0 and argv in a1.
57 * We do not expect the kernel to set up a complete stack frame,
58 * however.
59 *
60 * The MIPS ABI decrees that every caller will leave 16 bytes of
61 * space in the bottom of its stack frame for writing back the
62 * values of a0-a3, even when calling functions that take fewer
63 * than four arguments. It also requires the stack to be aligned
64 * to an 8-byte boundary. (This is because of 64-bit MIPS, which
65 * we're not dealing with... but we'll conform to the standard.)
66 */
67 li t0, 0xfffffff8 /* mask for stack alignment */
68 and sp, sp, t0 /* align the stack */
69 addiu sp, sp, -16 /* create our frame */
70
71 sw a1, __argv /* save second arg (argv) in __argv for use later */
72
73 jal main /* call main */
74 nop /* delay slot */
75
76 /*
77 * Now, we have the return value of main in v0.
78 *
79 * Move it to s0 (which is callee-save) so we still have
80 * it in case exit() returns.
81 *
82 * Also move it to a0 so it's the argument to exit.
83 */
84 move s0, v0 /* save return value */
85 jal exit /* call exit() */
86 move a0, s0 /* Set argument (in delay slot) */
87
88 /*
89 * If we got here, something is broken in exit().
90 * Try using _exit().
91 */
92 jal _exit /* Try _exit() */
93 move a0, s0 /* Set argument (in delay slot) */
94
95 /*
96 * If *that* doesn't work, try doing an _exit syscall by hand.
97 */
98 1:
99 move a0, s0
100 li v0, SYS__exit
101 syscall
102
103 /*
104 * ...and if we still can't exit, there's not much we can do
105 * but keep trying.
106 */
107 j 1b /* loop back */
108 nop /* delay slot */
109 .end __start